Conventionally, calcium carbonate has been incorporated at a high concentration in an application of plastisol obtained by mixing a vinyl chloride resin or an acrylic resin with a plasticizer and in a field of sealant obtained by mixing an urethane, a silicone resin, a polysulfide resin, and the like. On the other hand, among synthetic resins, for example, in a field utilizing high processing temperature such as a polyester resin typified by polyethylene terephthalate (PET) and an engineering plastic typified by polyamide (PA), polycarbonate (PC), or polyphenylene sulfide (PPS), a very small amount of calcium carbonate has been heretofore incorporated for the purpose of a light diffusing material an anti-blocking material, or the like.
For example, a porous white PET film, which is produced by a method of forming porous voids at an interface between a PET resin and a micropore-forming agent by a method for adding calcium carbonate whose particle size has been adjusted as a micropore-forming agent together with a non-compatible resin to a PET resin, and stretching the mixture into a film (sheet) (Patent Document 1), or a method for adding an inorganic fine particle such as barium sulfate to a PET resin, and stretching the mixture into a film (sheet) (Patent Document 2), has been put into practice in a wide variety of fields such as a synthetic paper, a (prepaid) card, a label and an optical reflecting film (sheet). Among them, for example, in the case of a light reflecting film utilized in liquid crystal TV application, high image quality, wide screen and low cost of liquid crystal TV are required.